Investigations of the mechanism of photoreception and transduction are proposed to enable us to elucidate the molecular basis of the visual process - that process by which a photon can elicit an electrophysiological signal to be transmitted to the brain. The special photoreceptors which carry out this process have a key macromolecule, the chromoprotein rhodopsin, which mediates this process. The essential chromophore is the Vitamin A retinaldehyde linked to the protein by a special Schiff base. Absorption of light by this chromophore triggers a series of events distinguished by their spectra called bleaching. Our objective is to elucidate the molecular nature of these events and associate them with the triggering of the cellular physiological response. The processes of photoreception and transduction are dynamic events all occurring within 1 millisecond. A series of kinetic experiments are outlined which will examine the primary photochemical event which occurs in picoseconds, the sequential series of spectral bleaching events which occur in nanoseconds to milliseconds, and the coupling of these series of events, such as to the release of Ca ions transmitter to affect the electrophysiological response, hyperpolarization of the photoreceptor plasma membrane. Three special instruments which are built for ultrarapid kinetic spectroscopy will be used to examine absorption of fluorescence changes on respective timescales of picoseconds, nanoseconds, and microseconds and longer. Experiments and techniques of this nature provide information critical to out understanding of the dynamic process of the visual response.